JP 2005-036711A, published by the Japan Patent Office in 2005, discloses a fuel pump which supplies fuel to an internal combustion engine.
The internal combustion engine comprises intake valves and exhaust valves as well as a camshaft which rotates in a fixed relation with the rotation of the engine to open and close the intake valves and exhaust valves. A crank sprocket is fixed to the crankshaft and a valve-driving sprocket is fixed to the camshaft. A timing chain is wrapped around the crank sprocket and the valve-driving sprocket to transmit the rotational force of the crankshaft to the camshaft. Valve-driving cams are fixed to the camshaft to open/close the intake valves and the exhaust valves when the camshaft is rotated by the rotational force of the camshaft.
The fuel pump comprises a pressure chamber delimited by a plunger. A lifter is fixed to the plunger and kept in contact with a fuel-pump-driving cam fixed to the camshaft together with the valve-driving cams.
When the engine operates, the camshaft rotates, and the fuel-pump-driving cam fixed to the camshaft causes the plunger to perform a reciprocating motion via the lifter such that the pressure chamber expands and shrinks alternately. When the pressure chamber expands, fuel is suctioned into the pressure chamber, and when the pressure chamber shrinks, the fuel in the pressure chamber is pressurized and discharged into a fuel passage of the internal combustion engine.